“Some people don’t choose to be the size they are – or height. If you have to pay extra money [for clothes] subliminally it feels like you are being told you have to lose weight,” she said.

However, Anna Scholz, a plus-size fashion designer, told the programme there was a limit to the size range that could be produced for the same price as it can take twice the fabric to make the same shirt for a larger size as a small one.

“As a company we sell from size 16 to 28 – if I had smaller sizes as well I would have to price them differently.”

Maria Wassell, a retail supervisor from Kent, spotted the discrepancy at her local New Look branch in Ashford in Kent.

She told the Sun newspaper: “It’s like I’m being discriminated against for being plus-size when I’m only slightly bigger than average.

“The average size for a British woman is now a size 16. Plus-size purchases are on the increase. If you look at the statistics, there’s more money being spent on plus-size clothing now then there was even three years ago.”

Ms Wassell said she used to work for a plus-size brand, and the argument that clothes for bigger sizes needed to be priced more highly was “basically rubbish”.

Emily Sutherland, features writer at fashion trade journal Drapers, also had little time for that explanation.

“Retailers may argue a larger size requires more fabric and is therefore more expensive to produce… or that there are subtle differences between straight and plus-size products that impact on price, but customers point out tall and maternity ranges, which also use more fabric, are rarely priced higher – and that smaller petite products are unlikely to be cheaper.”

She said harmonising prices between the ranges was becoming increasingly common.

New Look said in a statement: “We are in the process of reviewing the pricing structure of our Plus Size collection in a way which works best for our customers and our business.

“We are proud of the ranges we offer to our Plus Size customers and value all customers, no matter what their body shape or size.”